Black pigments used in coatings, inks, toners, rubbers/plastics, and so on are required to be excellent in characteristics such as blackness, hue, tinting strength, and is hiding power and yet inexpensive. Carbon black, iron oxide-based pigments typified by magnetite, and complex oxide-based pigments have been employed according to the use.
Typical examples of black pigments mainly comprising a metal oxide include particulates of single-metal oxides, such as manganese oxide and copper oxide, and complex oxides of these metal elements.
As disclosed in JP 2000-162643A, a light shield in black-matrix-on-array type plasma displays and plasma addressed liquid crystal displays is required to have high electrical resistance to prevent electrical conduction between electrodes, so is the black pigment used to form the light shield as a matter of course. However, a black pigment exhibiting both good blackness and high electrical resistance has not been proposed as yet.
A few types of cobalt oxide particulates have been proposed as a battery material (see JP 10-324523A and JP 9-22692A). JP 10-324523A discloses wet-process reacted tricobalt tetroxide particulates or a mixture of the tricobalt tetroxide particles and cobalt oxyhydroxide particles. JP 9-22692A discloses platy tricobalt tetroxide particulates. These cobalt oxides are produced for use as a battery material and are unsatisfactory in terms of blackness and high electrical resistance.